From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
The effects of removing the unloading delivery valve in a fuel pump and injector system.
| Identifier | ExFiles\Box 179b\3\ img101 | |
| Date | 1st February 1933 | |
| -11- EFFECT OF THE UNLOADING DELIVERY VALVE. An unloading delivery valve placed immediately above the pump chamber is a feature of the Bosch pump. Its function is to relieve the pressure in the fuel line prior to closing of injector by virtually increasing the capacity of the line. A rapid reduction of pressure in the fuel line assists in rapid seating of the atomiser needle and hence in the prevention of dribble at the nozzle. With a fuel line of such small capacity as that in the R.R. combined pump and injector, it appeared that a delivery valve of the unloading type was hardly necessary since the injector needle would function as a delivery valve. The removal of the delivery valve should increase the delivery by not more than the unloading capacity (40 cu.mm. in this case). The delivery valve was accordingly removed. This resulted in a small increase in the volume of oil under compression as the space normally occupied by this valve was not filled up. The effect of removing the valve on delivery is shown in Fig.10. The tests were conducted on the pump with hole No.3 (at 120° to supply pipe) unplugged. The discharge at maximum injection increased by approximately c10 ccs/cycle, showed a slightly less marked tendency to fall off at the lower speeds, but otherwise showed similar characteristics to the curve taken with the valve in place. The spill was practically unaffected by the change. The Discharge-Control position curve, Fig.11, indicates that the only effect is to increase the delivery for a given control position. The increase is approximately the same for all control positions. Removing the delivery valve has an appreciable effect on the lag as may be seen from Fig.12 especially at the lower speeds. The injection period is from 2° to 3° shorter without the valve than with it from 1000 R.P.M. down to 500 R.P.M. The lag and injection period were measured at normal injection. Hence, from these tests it is concluded that the general performance of the pump is improved by removing the unloading delivery valve. The improvement may be still greater when the space normally occupied by the delivery valve and its spring is filled up and a suitable connection made with a small passage leading direct from the pump chamber to the injector. It may be noted in passing, while the capacity of the unloading valve is 40 cu.mm. the increase in delivery due to its removal was only 10 cu.mm. The reason for this is not at present apparent. | ||